[Fot] TR4A front suspension.

Tue Mar 10 11:51:14 MDT 2015

I know of your article in Kas Kastners Triumph Preparation Handbook and on
my TR3 I could eliminate the bump steer completely with laser and mirror
after fitting a small steering rack (TR7 rack if I remember).
On the TR4A, bending the steering arms to the outside and thus making the
track rods 1cm longer improved things a little bit. Also lowering the rack
by 0.3cm is a little better. Moving the rack to the rear or to the front is
making the bump steer worse. Maybe fitting a smaller steering rack (distance
between the inner balljoints) can eliminate the bump steer further?
Marcel

  _____  

Van: Bill Babcock [mailto:Bill at ponostyle.com] 
Verzonden: zondag 8 maart 2015 23:18
Aan: Van Mulders Marcel
Onderwerp: Re: [Fot] TR4A front suspension.

Geometrically, zero bump steer is achieved when the centerline of the upper
and arm lower pivots are in line with the steering linkage pivots, both
inner and outer and the centerline of the tie rod intersects with the
instant center of the upper and lower arms. This isn’t actually achievable
with a trunnion linkage. I got almost all of the bump steer out of Peyote by
getting the centerlines right and then moving the rack up and down while
bouncing a laser off a mirror on the control arm onto a target on a wall.  

On Mar 8, 2015, at 11:35 AM, Van Mulders Marcel via Fot <fot at autox.team.net>
wrote:

In June 2014 I bought Bob Kramer's TR4A racecar after I crashed my TR3 at
the Zandvoort circuit (The Netherlands). It's a great car and it will get
better. Of my TR3, I only kept the engine and overdrive dogbox  Overhauling
the front suspension, I found that the lower trunnion was moving on the bolt
instead of the bushed lower wishbones : the distance pieces in the wishbones
where shorter than original, so the trunnion was not clamped by these
distance pieces when fastening the bolt. Correcting this, the upright has
less play now, only a little in the trunnion, and this upright with
balljoint can't be forced anymore between the outer ends of the upper
wihbones, the balljoint is 1/2" too far to the rear. Turning the upper
wishbones to the rear (by moving the fulcrum pin) isn't a good option,
because binding will occur. I've drilled new holes for the brackets for the
inner ends of the lower wishbones : the suspension is moving without any
binding now but I don't know if I will leave it like that. I wonder if
something is wrong with the uprights? (less than 3° caster?) If I measure
the caster, I find 2.2° on both sides, but probably that isn't proving
anything. The chassis is as new, no damage. Any idea's someone?
Another question : trying to get at zero bump steer, the best I get at by
moving the steering rack is a J : the wheels are toeing in when lowered more
than 3 cm below ride height (minimal to 5cm, then more and more toe in).
Bending the steering arms to the outside, almost touching the brake disks
now, has straightened the J a little.  Is it possible to eliminate the bump
steer completely, or have we(TR4A-TR6) to accept some bump steer in the
least important part of the suspension travel?
Marcel.
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